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Analysis of High Power LED Tunnel Light application

1. Comparison of conventional tunnel lights and LED tunnel lights
Currently tunnel lighting are mostly high pressure sodium lamp as the light source, but high-pressure sodium lamp radiation in the form, the color, the visual sensitivity characteristics, power specifications, brightness control, etc. are many deficiencies, and the emerging LED tunnel lighting with its excellent performance in particular brightness controllability to overcome many deficiencies of HPS is becoming the mainstream of the world tunnel lighting fixtures.

LED is a semiconductor light emitting technology. Developed the first LED can emit red light. Lights used in electronic devices. With the development of technology, now has LED lights can emit various colors of light, and is widely used in many types of industry, the main application markets, including the traditional market display and lights, backlight market, street lights, tunnel lights, automotive lighting market outdoor landscape lighting market and interior lighting, specialty lighting market. LED light source at the tunnel has its unique advantages.

(1) LED Tunnel Light Low power consumption, energy-saving, compared to traditional high-pressure sodium lamp, saving more than 40% of its energy consumption.
(2) LED tunnel lights, long life, there are 100,000 hours under ideal conditions, and high-pressure sodium lamps and fluorescent tube life of only 10,000 hours to 30,000 hours.
(3) LED tunnel lights high reliability, low maintenance and routine maintenance costs, the average time between failures of up to 30,000 hours, while the average high pressure sodium lamps and fluorescent tubes time between failures is less than 10,000 hours.
(4) reduces the power distribution system (cables, transformers, power distribution box, bridge, etc.) of the construction costs for the long tunnel, the case of long distance power supply, cables, power distribution facilities, especially large proportion of the cost, LED tunnel investment saving lamp can be greatly reduced because the cables and power distribution equipment and the like.
(5) LED tunnel lights can achieve instant start, easy to adjust brightness, with no flicker, a wide range of start-up voltage, etc., can achieve a variety of power-saving modes, such as adjusting the illuminance according to the road, intelligent traffic tunnel.
(6) high pressure sodium lamps, fluorescent lamps, lamp contains mercury, lead and chemical pollutants, and LED tunnel lighting source without chemical polluting substances, is a green light.

2. High-power LED tunnel lights design requirements
(1) Whether the tunnel is required to set up the basic day or night lighting. During the day, the vehicle enters the tunnel, surface brightness should be gradually decreased, so that the driver's vision of a process of adaptation, the entrance into the introductory section, segment adaptation and transition.
(2) determine the lead-in, adapt the length (S) section and the transition section, usually according to the vehicle speed (V) with T = 2s adaptation time to determine the available S = VT / 3.6m to estimate; outlet sections should also be set up transition lighting, two-way traffic in the same situation and the inlet section.
(3) does not strengthen entrance nighttime lighting, street lighting should be located outside the cave, the cave basic brightness not less than 1/2 brightness; emergency lighting should be located inside the tunnel, the brightness is not less than 1/10 of the basic brightness.

3. High Power LED Tunnel Light design
Select 3.1 LED light source
LED lumen output is to determine the LED tunnel lights are of practical value of the basic indicators, according to the requirements, LED tunnel lights used lumens LED's single wattage should reach 80 lumens or more, after nearly three years of LED luminous efficiency of the high-speed after the development stage can supply large quantities of LED luminous efficiency has reached 90lm / W or more, and are continuing to increase brightness.

3.2 optical designs
According tunnel lighting requirements, depending on the lighting sections with different light fixtures, according to the optical principle and the LED light source with high directivity characteristics, the reasonable light distribution in the case of meet luminance or illuminance requirements, reduce lighting power, reach energy saving purposes.

(1) The introduction of paragraph of the tunnel inlet section, segment adaptation and transition section and an outlet section with asymmetric light distribution illumination (back light), under the same illumination conditions, compared with the general lighting can improve the surface brightness 121%, at the same time using the advantages of high directivity, and strictly control the light intensity of large angle direction to eliminate most of the glare.
(2) in the basic section of the tunnel, the current common light distribution types are concentrating light, side light-emitting type, Lambertian light distribution and the like. Different applications to apply different forms of light distribution.

Example: road lighting should choose a bat wing light distribution, lighting should use a concentrating light. Due to the special nature of tunnel lighting, tunnel lighting fixtures arranged density is very high, so the tunnel lighting fixtures from a secondary light distribution is different from the general road lighting. In tunnel lighting bat wing light distribution, Lambertian light distribution is able to meet the requirements of illumination uniformity, which is mainly due to the light from the tunnel lighting is relatively small.

3.3 Thermal Design
LED is a photovoltaic device, the current high-power LED in the forefront of the world, the course of their work, only 15% to 20% of electrical energy into light energy, most of the rest of the energy is converted into heat, so that the LED temperature. On the other hand, LED lumen output as the LED junction temperature increases and decreases, while the LED junction temperature rise as life expectancy shortened. Therefore, the LED's heat is well handled well will be directly related to the use of tunnel lighting effects and life.
Currently radiating power LED There are three main ways:
① Natural cooling, install a fan forced cooling and heat pipe heat sinks plus technology. Natural cooling using natural convection and heat radiation, reliable structure, easy to do water. But light body structure design itself is demanding.
② Install a fan forced cooling main advantage of forced convection cooling, thermal spreader speed, but the high cost and noise, Waterproof difficult.
③ Plus fin heat pipe heat pipe technology mainly uses the heat generated by the LED rapidly conducted to the heat sink and cooling purposes, no moving parts, the system is stable, but the cost is relatively high.

Since the tunnel compared with the general road, has its own unique properties, we use heat pipe heat sink technology plus the way the heat treatment, hot channel vertical design, modular cooling mode, the LED junction temperature is maintained below 70 ℃, guarantee LED low light decay time stable work, improve lighting maintenance factor, saving maintenance costs.

According to the flow characteristics of the airflow, in the tunnel, cooling chamber asymmetric ventilation design to ensure air convection cooling, while reducing soot and other pollution produced quality cars into the cooling chamber, adsorption heat dissipation structure results in reduced cooling efficiency.

3.4 Design
The use of lightweight aluminum case, lightweight 10kg or less. LED light source cavity and electrical chamber according to IP65 protection grade design, cooling chamber design according to IP23; the light source chamber and heat isolation chamber using a reasonable way to avoid mutual influence of the light source chamber and the cooling chamber heat flow. Since the air does not flow in the tunnel, in which the vehicle exhaust doping component complex, LED tunnel lighting should have good corrosion resistance, external exhaust gas, smoke and other chemical substances contained in the atmosphere inside the tunnel, each structural component surfaces are protected against corrosion treatment to meet the corrosion requirements.

3.5 Circuit Design
LED forward voltage characteristics similar to ordinary diode, plus the forward voltage varies slightly, it will have a significant change in forward current, resulting in LED internal heat losses and rapid increase, seriously affecting the normal work and life of the LED. To prevent this from happening, high-power LED constant current power supply must generally. In order to maximize the efficiency of the current source, reducing the heat input voltage, the current source must be reasonable control, so that the maximum value after deducting internal voltage drop, like the current, but also match the total LED voltage required. Internal loss, and reliability to the current source is guaranteed.

Tunnel lighting generally requires a lot of lamps, power consumption is huge, to save energy and reduce the power grid "pollution", LED tunnel lights drive also requires the power factor and harmonic generation must meet the relevant standards, with due consideration to electromagnetic interference and electromagnetic compatibility.

(1) high conversion efficiency, high stability of the power conversion efficiency greater than 87%, power factor greater than 95%, against external voltage fluctuation ability of the switching power supply (96 ~ 264V), together with the constant current circuit design, to constant current to drive the LED light source, to ensure the LED life.

(2) the use of a control circuit for tunnel lighting, lighting the lamp according to different segments and in different time tunnel power adjustment to achieve good lighting effect and energy saving. The introduction sections of the tunnel inlet section, the middle section, transition section and an outlet section with different current drive to make it as close to the curve of the tunnel lighting requirements, to achieve the best lighting effects; import and export sections of the tunnel section with a timing adjustment function light adjusted by adjusting the output current PWM or dual power supply, single power supply places at night to power reduction of 50% of daytime illumination, both during the day and night, are effective in reducing "light hole" and "black hole "phenomenon.